1. Field of the Invention
The present invention relates to an insulation state detecting device that detects a ground fault or the insulation state on a ground potential on the basis of the charging state of a flying capacitor.
2. Description of the Related Art
Electric vehicles and plug-in hybrid vehicles (PHVs) have been put into practical use and various types of such vehicles have been put on the market. In such vehicles, electric power is used as a power source and a high-voltage (200 V, for example) DC power source needs to be insulated from a vehicle body. An insulation state detecting device plays an important role, which detects a ground fault or the insulation state on a ground potential portion (ground potential) of such a DC power source.
This type of insulation state detecting device includes an already-known device with a flying capacitor charged by a DC power source. This insulation state detecting device charges the flying capacitor with a positive potential or a negative potential of the DC power source and measures the charging voltage by using a microcomputer, thereby detecting ground fault resistance or the insulation state on the positive-pole side or the negative-pole side.
For typical measurement of leakage of electricity on electric vehicles as described above, for example, high accuracy of measurement is focused on in terms of excluding erroneous detections. Various types of technologies have been developed for that purpose (refer to Japanese Patent Application Laid-open No. 2010-239822 and Japanese Patent Application Laid-open No. 2011-017586, for example). With the technology disclosed in Japanese Patent Application Laid-open No. 2010-239822, a ceramic capacitor is used as a flying capacitor, thereby achieving both the downsize of a measuring device and the insulation resistance measurement with high accuracy. With the technology disclosed in Japanese Patent Application Laid-open No. 2011-017586, suppressing effectively any erroneous detection to be generated due to noise components during the measurement is achieved.
As disclosed in Japanese Patent Application Laid-open No. 2010-239822 and Japanese Patent Application Laid-open No. 2011-017586, a typical insulation state detecting device (a leak measurement means) in which the detection accuracy is focused on takes an important role in particular when a vehicle is normally used. The technology focusing only on the detection accuracy as described above, however, is not sufficient for an unexpected situation where any leakage failure such as an accident occurs. Another technology has been therefore desired for determining important matters including the possibility of an electric shock in a time period as short as possible, rather than the determining technology focusing on the detection accuracy.
In view of the conventional circumstances, the present invention aims to provide a technology for solving the issues described above.